Semiconductor wafers for an IC or LSI are subject to an inspection for electrical connection or the like after its manufacture. The inspection is conducted under an atmosphere of high temperature, 150° C. to 200° C., which is higher than the usual operation temperature of the semiconductor wafer, so that defective products may be removed in a short time by the accelerated test. Therefore, this test is called a burn-in test, and the material used in the inspection equipment for the test must have heat resistance. On the other hand, in the case of a device for a motor vehicle or the like, an inspection is conducted at a temperature of −30° C. or less because operation security under cryogenic temperature is required of the device; therefore the material used in the inspection equipment for such inspection must have cold resistance.
The burn-in test of a semiconductor wafer is performed through electrodes on the surface of the semiconductor wafer. In that case, since the height of the electrodes as well as the height of the electrodes of the inspection equipment is varied, it is necessary to eliminate a contact failure due to the variations in the height of the electrodes. Therefore, the inspection is done with a soft flat conductive sheet put between the electrodes. This conductive sheet has conductive parts which are arranged along the pattern of the electrodes on the semiconductor wafer surface and which are insulated in the surface direction such that conduction is achieved in the thickness direction at the conductive parts while no conduction occurs between the electrodes. Therefore, this sheet is called an anisotropic conductive sheet. The anisotropic conductive sheet is used not only for the inspection of a semiconductor wafer but also for eliminating a contact failure due to variation in the electrode height when a packaged semiconductor wafer is mounted on a printed circuit board or the like.
Examples of packages housing semiconductor wafers include a surface mounting-type package, such as BGA or LGA, and a through hole mounting-type package such as a pin grid array (PGA). Of these packages, the BGA is structured such that ball-shaped electrodes are arranged in array on the rear surface of a package so that the ball-shaped electrodes are used instead of a lead wire. Thus, when the package is used, it is pushed against the anisotropic conductive sheet so as to achieve sufficient connection.
FIG. 5 is a diagram showing a structure and mounting condition of a conventional anisotropic conductive sheet. FIG. 5 illustrates examples of anisotropic conductive sheets used for a connection of bump electrodes such as a BGA (see Japanese Patent Application Publication No. H 10-221375 (Patent document 1)). FIG. 5(a) is a sectional view of the anisotropic conductive sheet before mounting a semiconductor wafer, and FIG. 5(b) is a sectional view showing a condition after the mounting of a semiconductor wafer 56. As shown in FIG. 5(a), this anisotropic conductive sheet 50 is constituted by an insulative part 51 consisting of a flexible film made of an insulative resin such as polyimide, polyester, or the like, and a conductive part 52 made of copper, gold, or the like. In the insulative part 51, a connection hole 53 is formed in the shape of a truncated cone at the same position as a bump electrode 57 of the semiconductor wafer 56.
Once the semiconductor wafer 56 is mounted, as shown in FIG. 5(b), the bump electrode 57 of the semiconductor wafer 56 is inserted into the connection hole 53 and touches the conductive part 52, which results in conduction. Also, it is stated that even if the semiconductor wafer 56 is pressed onto the sheet, the conductive part 52 will be prevented from being damaged because the pressing force will disperse without concentrating onto the conductive part 52 since the bump electrode 57 is supported by touching with the wall face of the connection hole 53. It is also stated that the electrical connection can be ensured further by providing a protrusion 58 such as a metallic pin or the like on the conductive part 52 at the bottom of the connection hole 53 as shown in FIG. 5(c).
[Patent document 1] Japanese Patent Application Publication No. H 10-221375